The present invention relates generally to optical encoders. More particularly, the present invention relates to optical encoders having various orientations.
Optical encoders detect motion and typically provide closed-loop feedback to a motor control system. When operated in conjunction with a code scale, an optical encoder detects motion (linear or rotary motion of the code scale), converting the detected motion into digital signal that encode the movement, position, or velocity of the code scale. Here, the phrase “code scale” includes code wheels and code strips.
Usually, motion of the code scale is detected optically by means of an optical emitter and an optical detector. The optical emitter emits light impinging on and reflecting from the code scale. The reflected light is detected by the optical detector. A typical code scale includes a regular pattern of slots and bars that reflect light in a known pattern.
FIGS. 1A through 1C illustrate a known optical encoder 100 and a code scale 120. FIG. 1A is a cutaway side view of the optical encoder 100 and the code scale 120. FIG. 1B is the code scale 120 as viewed from the optical encoder 100. FIG. 1C is the optical encoder 100 as viewed from the optical encoder 100.
FIGS. 1A through 1C include orientation axes legend for even more clarity.
Referring to FIGS. 1A through 1C, the encoder 100 includes an optical emitter 102 and an optical detector 104 mounted on a substrate 106 such as a lead frame 106. The optical emitter 102 and the optical detector 104 as well portions of the lead frame 106 are encapsulated in an encapsulant 108 including, for example, clear epoxy. The encapsulant 108 defines a first dome-shaped surface 110 (first lens 110) over the optical emitter 102 and a second dome-shaped surface 112 (second lens 112) over the optical detector 104.
The optical emitter 102 emits light that leaves the encapsulant 108 via the first lens 110. The first lens 110 concentrates or otherwise directs the light toward the code scale 120, the light reflecting off of the code scale 120. The reflected light reaches the optical detector 104 via the second lens 112. The second lens 112 concentrates or otherwise directs the reflected light toward the optical detector 104. The optical detector 104 can be, for example only, photo detector that converts light into electrical signals.
In the illustrated example, the optical emitter 102 is a slit-type light emitter, the slit along the Y-axis. As illustrated, the optical detector 104 is placed along the Y-axis. Further, the slots and bars of the code scale 120 runs along the Y-axis.
Accordingly, the optical encoder 100 and the code scale 120 are oriented and positioned relative to each other in order to detect movements of the code scale 120 in the X-axis direction.
This design has several weaknesses. For example, the optical encoder 100 is sensitive to misalignments. Even slight misalignments of the slit emitter 102 lead to contrast degradation, thus degradation of the performance of the optical encoder 100. Further, the optical encoder 100 detects movements in only one direction (for example, along the X-axis direction in the illustrated example), limiting flexibility in orientation of the encoder package. Moreover the existing optical encoder has limited number (typically at most two) of data channels on one side of the emitter.
Accordingly, there remains a need for improved optical encoder that alleviates or overcomes these shortcomings.